Conventionally, deceleration mechanisms using planetary gears are widely used in various technical fields.
For example, Japanese Patent Application Laid-open No. 2002-349643 (paragraphs [0026] and [0027], FIG. 1) describes a deceleration mechanism including a rotatable sun gear, a planetary gear that revolves around the sun gear while rotating, and a planetary carrier that converts the revolution of the planetary gear into rotation of a sun gear in the next stage. The deceleration mechanism is formed by superposing the sun gears (including input axis) and the planetary gears and planetary carriers (including output axis) in three stages in an axial direction, and decelerates the rotation of a rotation axis (input axis) of a motor in a stepwise manner and takes out the rotation from the output axis.
Incidentally, in the deceleration mechanisms used in precision equipment or the like required for control with high precision, a high deceleration ratio is required in many cases. However, if a high deceleration ratio is intended to be obtained using the structure of the deceleration mechanism in Japanese Patent Application Laid-open No. 2002-349643, it is necessary to superpose the planetary gears and the like in the axial direction in many stages. Further, if a high deceleration ratio is intended to be obtained without increasing the number of deceleration stages, the width in a radial direction becomes large, and there arises a problem that the downsizing is difficult.